The present study explored fear acquisition in differential delay versus trace conditioning in regard to the potential role of the acquired contingency awareness. One of two neutral pictures (CS+) either coterminated with (delay group; n=32) or was followed by the aversive unconditioned stimulus (UCS) after CS offset (trace group; n=32), while startle blink and skin conductance responses (SCR) were measured. As expected, the acquisition of conditioned startle potentiation in delay conditioning was independent of contingency awareness. In contrast, fear-potentiated startle in trace conditioning was only observed for those participants who were aware of the CS-UCS contingencies. SCR conditioning was generally only obtained for aware participants. The present results suggest a more implicit learning process in delay fear conditioning, whereas the explicit acquisition of contingency awareness might be a prerequisite for trace fear conditioning.